Up to speed: why processing speed deserves a proper look in dyslexia assessment
Picture a child who can tell you every sound in the word "splash." They can blend sounds together, segment them, manipulate them, all the skills we associate with strong phonological awareness. And yet they still read slowly, they still take twice as long as their classmates to get a sentence down on paper, and homework that should take twenty minutes stretches into an hour of tears.
For years, a case like this might not have been picked up as dyslexia at all. If phonological awareness looked fine on paper, the door to assessment often stayed shut. But we now know that phonological awareness is only part of the picture. Processing speed is another piece, and it is time it got the attention it deserves.
What do we mean by processing speed?
Processing speed is exactly what it sounds like: how quickly someone can take in information, make sense of it, and respond. In a literacy context, this shows up in tasks like rapid automatised naming (RAN), where a child is asked to name a string of familiar objects, colours, or letters as fast as they can.
It sounds like a small thing. It is not. Slow processing speed affects how quickly a child can retrieve a letter sound, recognise a whole word, or get their ideas from brain to page. Even when the underlying knowledge is there, the speed of access can let a child down again and again.
How this plays out in reading and writing
A child with slow processing speed might:
Read accurately but painfully slowly, losing the meaning of a sentence because so much effort goes into decoding each word
Know a spelling rule perfectly well in isolation but freeze when trying to apply it at speed during independent writing
Run out of time in tests, not because they do not know the content, but because they cannot retrieve and produce it fast enough
Appear inconsistent, doing beautifully on an untimed task and falling apart the moment a clock is involved
None of this is about effort or motivation. It is about the mechanics of how quickly information moves through the system. And it can exist quite separately from phonological awareness, which is exactly why the old model of dyslexia often missed these children entirely.
The old definition and its blind spot
The Rose definition, which shaped so much of UK practice for years, placed phonological awareness front and centre as a defining feature of dyslexia. This was useful in many ways. It gave assessors a clear marker to look for. But it also created an unintended gatekeeping effect. If a child's phonological awareness tested as broadly typical, some assessors and schools took that as evidence the child could not be dyslexic, regardless of how much they were struggling with reading fluency, spelling, or written output.
Let's be honest, this never quite matched what practitioners were seeing in real life. Plenty of children with clear, persistent literacy difficulties simply did not fit that narrow phonological box.
Enter the Delphi consensus definition
The new Delphi consensus definition widens the lens considerably. Rather than treating phonological awareness as a required gatekeeper, it recognises dyslexia as a difficulty that can involve a range of underlying processes, including processing speed, working memory, and orthographic processing, alongside phonological skills.
This matters enormously for assessment. It means a child does not need to fail a phonological awareness test to be considered for a dyslexia assessment. If they are showing significant, persistent difficulty with reading fluency or writing speed that cannot be explained by other factors, that is a legitimate reason to look closer, even if their phonological awareness looks solid.
Why this shift is good news for families
If your child has always seemed to "get it" when you explain something, but never seems to get it down on paper in time, this shift matters. It means assessors are now expected to look at the whole profile, not tick one box and stop there.
It also means fewer children slipping through the gaps because their difficulty did not present in the one way an older model expected it to. Processing speed difficulties are real, they are measurable, and they deserve the same weight as phonological awareness when we are trying to understand why a capable child is struggling with literacy.
The takeaway
Dyslexia has never been one single thing with one single fingerprint. The Delphi definition brings assessment practice closer to what families and teachers have long suspected: that slow processing speed, on its own or alongside other difficulties, can be enough to warrant a proper look. If your child is bright, articulate, and still struggling to get words onto a page in reasonable time, that is worth taking seriously, whatever their phonological awareness scores say.
